Prop Queston: HC 12x20-8

Jonathan Baron

Jonathan Baron

New member
Bad news: that fragile back-plate for the spinner on my 14-19 finally decided to crack beyond what stop drilling has so somewhat accomplished over the past half century.

Good news: I have been keeping a *new* one for just such an occasion for the past 6 years. I would have kept it in a safety deposit box were it smaller.

Question: First the prop must come off before the old plate can be removed and a fresh plate added. Russell is off somewhere in the Pacific at the moment....some group of Islands that are, strangely, a United States state (don't ask me how the heck THAT happened) and I can't ask him. What tool do you use to remove that massive castle battlement of a nut that holds the prop on, what torque should it set to when it's put back on, and what tool - or method - can you use to apply/check the torque setting?

It's the infamous Hartzell HC 12x20 found on 14-19s, Cruisairs with O-435 conversions, and many Navions.

For those of you who actually know me, fear not: an actual mechanic will be performing the work.

Jonathan
 
I have a 3 ft steel breaker bar I use on the Navion. The torque is tighten it up till it bottoms then 1/2 turn works every time its on and off-------ALOT. My Navion couple gave me a great shirt and hat from Hartzell---I don't wear them. In silver Lynn N9818B Old Russell :lol: sure gets around!
 
I use a 4' long pry bar from Matco Tools. It looks like a screwdriver but is stamped "NOT TO BE USED AS A SCREWDRIVER".
That and a dead blow hammer will loosen the nut. Torque is the old German method "goot-n-tight" and line up a safety hole.
 
Thanks guys...you were the folks whom I'd really hoped would see this and respond. Joe, you've done this before on my very airplane and Lynn, you just know stuff, as does Joe: stuff, defined here as diverse knowledge of the vanshing mystic old airplane arts :)

BTW, I am finally have LOTS of FUN with the aircraft at long last. I remain astonished how well these Triple Tails make such graceful allowances for rusty - or just average - pilots, unlike Luscombes who feel they must punish you, after a lapse, and demonstrate EVERY FLAW IN YOUR FLYING TECHNIQUE before they calm down and relectantly forgive you.

Jonathan
 
Yanked the prop last night....that nut went beyond German goot-n-tight. Must have been tightened by friggin Spartans...dang near tossed my poor mechanic into the pit of death when it finally let loose. I imagined King Leonides yelling, "This...is...SPARTA!" when it kicked.

The crack in the backplate, and the chunk that blew out, had deformed the plate when the prop was spinning, causing it to rub mightily on those guide mounts behind it. Fortunately the plate is made of softer stuff. I'll be back in the air this weekend :)

Jonathan
 
Just reinstalled my prop after overhaul. 485 foot pounds So a 242 pound guy on a 2 two bar. I have the data if ya want it.


BTW Jonathan, I am writing a Jonathanesc story about my near disaster.

Tailwinds
Ben
 
LOL Ben!

I *finally* fired off mine to Robert this morning, though this one is not another "Lament the man who falls for a hangar queen," tale of the anguish of unrequited love :)

The prop went back on the grinning face of my 'Master last evening, complete with people hoisted off their feet while holding onto either a prop blade or a bending crowbar. It went much more smoothly than the removal which featured me banging said bending crowbar with a trailer hitch. Just meeting Joe's German standards with the proper fine adjustment tools.

Jonathan
 
Interesting twist in this strange bit of business.

This Hartzell Hydroselective prop has some mechanical oddities. The hub (with plate and spinner attached) moves forward when the blades are positioned to low pitch and back for high pitch. A control cable moves a heavy brass dome fore and aft to accomplish this, and an oil filled diaphragm supports the effort from behind. Spacers (brass washers) behind the dome control the rear position limit of the dome, allowing it to be positioned properly for each sort of installation.

This was working fine when Joe Sills did the major on my O435. He reinstalled it correctly. After that business of the gear refusing to come down after the annual performed by Reliant Aviation in Albany Oregon, the prop had to come off, of course, along with the usual other stuff (engine tear-down, repairs and such). A nearby prop shop did the prop work promptly. Reliant, may-they-crash-in-a-remote-desert-and-slowly-die-of-thirst, let the project sit so damned long, though, that they did not discover that the prop was indexed improperly until after the prop repair warranty had expired. They could not achieve high enough RPM, and didn't want to spend money to send it back to the shop. So they tried other things before eating the cost of sending it back to the prop shop. Out came all but one of the spacers. This wasn't enough to "fix" the problem. The prop had to be sent back, came back, was assembled, but the spacers were not replaced. Not only did this take the pitch range out of tolerance (low pitch was 6 degrees instead of the 11 degrees specified in the TC for that prop with that blade type), it made the plate rub against the engine when set to cruise. By the time there was any aural symptom of the problem, the plate was pretty chewed up and not far from separating. Little imagination is needed to see nasty outcomes from that scenario.

There were other signs of a problem. Full throttle max bite RPM was 2450 but this says "may need adjustment" rather than "it's FUBAR and could come apart at any time."

I would conclude this post with something typical like, "You might want to check this if you have an HC 12x20-8 or -8C," but I doubt you'll find something like this on your airplane. Although the likelihood of finding a shop that understands your Triple Tail is low, few of them will try to kill you to save a few bucks.

Interesting system though. I'm trying to learn more about how things work on these machines, and my current mechanic patiently takes the time to show me each thing, and tell me how it works. What really takes patience is making sure I actually understand after he's explained something to me :roll:

I have finally concluded (about time) that not knowing how things work presents far more danger to to me as an owner of a Triple Tail than anything I could ever encounter in flying it. There is an attitude out there that too many mechanics possess: if it has wings I can fix it. Of these, many will not confess - even to themselves - that they don't know something, pause, and find someone to ask who does. Nowadays I wonder how many pilots lie in the ground, or have had their ashes cast to the wind, who perished solely due to this attitude. That may be a tad dramatic. Most victims, I'm sure, only suffered inconvenience, a laundry emergency, or a lost airplane. Nobody in aviation maintenance actually sets out to hurt anyone.

Jonathan
 
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